The present application relates to a pretensioner and a seat belt apparatus for restraining an occupant with a seat belt by withdrawing a seat belt buckle on an occasion when the speed of a vehicle is suddenly decreased.
A seat belt apparatus for restraining an occupant has been provided to a vehicle seat, the seat belt apparatus restrains the occupant when the vehicle experiences a sudden change in momentum such as in a sudden stop, a collision, an impact, etc. Such a seat belt apparatus is normally provided with an emergency locking retractor (ELR), which does not restrain an occupant's motion during normal driving, but locks a seat belt retracting shaft only at an occurrence of a vehicle collision to prevent a seat belt from being further delivered. This ELR serves to prevent a seat belt from being further delivered by locking the retracting shaft thereof within an extremely short time when a deceleration exceeding a predetermined value is detected.
However, even though the retracting shaft is locked, the seat belt may be wound loosely on the retracting shaft. Such a device as an ELR may still allow the loosely wound belt to be withdrawn from the retracting shaft as the belt restrains an occupant. It is preferable to reduce, as much as possible, such a delivery of a seat belt due to looseness of the seat belt or a time lag until a retracting shaft is locked.
Hence, a pretensioner may be provided to offset such a delivery of a seat belt due to looseness of the seat belt or a time lag, to some extent, until a retracting shaft is locked. The pretensioner is configured to retract a seat belt buckle if a predetermined deceleration, similar to that in the case of locking operation for the retracting shaft, is detected. One such device is described in Patent Publication No. WO 2003-018374 (FIG. 2 and FIG. 5).
The pretensioner includes a wire, one end portion of which is connected to a seat belt buckle and the other end portion of which is fixed to a piston in a cylinder, and a housing, that holds the cylinder as well as guides the wire toward the direction of the cylinder. The wire is bent at its middle portion When a vehicle deceleration is detected, a high-pressure gas is jetted into a gas chamber formed in the housing and thereby the piston slides in the cylinder to withdraw the wire.
In the above described pretensioner, however when the pretensioner is not activated, if an excessive load is applied to the seat belt buckle such that a tongue is pushed in to the seat belt buckle with a strong force, or a baggage or an occupant is loaded on the seat belt buckle, the wire is pushed in along the direction of the cylinder.
Accordingly, the pretensioner and a seat belt apparatus disclosed herein below is configured to prevent a wire from being pushed in even when an excessive load is applied to a seat belt buckle.